Build WiFi Range Extender from 18" Parabolic Dish, construction pictures + instructions

Discussion in 'Wireless Internet' started by ac6tsxx, Apr 18, 2007.

  1. ac6tsxx

    ac6tsxx Guest

    Build A Tin Can Waveguide WiFi Antenna In One Hour. Then put it on a
    18" inch direct tv dish, (optional). No coax signal loss. I use a USB
    device on antenna, so only a usb cable feeds my computer. With 16' USB
    REPEARER CABLES end-to-end you can run 80 feet of cable without loss.
    Complete instructions. This Powerful wlan antenna REALLY KICKS BUTT!!

    Here is my version of the dish conversion to wifi range extender->

    ac6tsxx, Apr 18, 2007
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  2. ac6tsxx

    ac6tsxx Guest

    I am only running 32 feet, (2 cables), from my living room to my radio
    room dish. I quoted the 80 ft specs from the packages, but have not
    tried that run distance. No need here. I just took their word for it.
    Thanks for your info. That is important.

    ac6tsxx, Apr 19, 2007
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  3. Nicely done. You might want to add some numbers.

    Maximum gain for a 0.6meter diameter dish:
    gain = 9.87 * Dia^2 / wavelength^2 * (feed efficiency)
    gain = 9.87 * 600mm^2 / 125mm^2 * 0.4
    gain = 91
    dBi = 10 log(91) = 19.5dBi
    The 40% efficiency (that's the 0.4) is probably optimistic.

    However, that's the best that can be done. With a mismatched feed
    (your USB contraption), you'll be radiating much of the signal into
    all manner of undesireable directions, with very little hitting the
    dish and being reflected in the desired direction. That's why feed
    point "illumination" is important. Ideally with a properly matched
    feed, you'll get the same gain in xmit and recv. However, with your
    USB device feed system (an almost hemispherical feed pattern), all of
    the signal arrives at the feed in receive, but much of the signal goes
    nowhere useful in xmit. So, you'll get somewhat less than the
    theoretical 19.5dBi gain in receive, but xmit will be far less gain.

    Might was well guess how much less. Assuming a hemispherical pattern
    from the USB antenna, only about 10% of the RF hits the dish. The
    rest goes off in useless directions. So, 10% is:
    loss = 10 log(0.1) = -10dB
    So, my guess is that the antenna gain in xmit is about:
    19.5 - 10 = 9.5dB
    Yech. (I can produce a more accurate number for the 10% later but I
    don't have a DBS dish to measure handy right now).
    Jeff Liebermann, Apr 19, 2007
  4. Sigh. Sorry, I goofed. I was looking at a variety of DBS dish
    reflectors on other sites and got your construction mixed with another
    one that did NOT use a can type feed. My comments about different
    gain in xmit and receive apply only to building it without the tin
    can. If the can feed illumination pattern is reasonably well matched
    to the diameter of the dish, the tx and rx gains should be the same.
    My appologies for the wrong info.
    Jeff Liebermann, Apr 19, 2007
  5. ac6tsxx

    dold Guest

    The tin can was cut to 3-1/2 inches, which seems too short to me.
    with a 4" diameter can, I think the radiator should be at 1.7", but I would
    like to see the can at 5.5" as a standalone can.

    Should the radiator be at the focal point, or the mouth of the can
    (properly sized for its own radiator)?

    And where might we assume that the radiator is on that adapter? It looks
    like it might be in the middle of the bore, which is good, but that's an
    awfully large hole in the side of the can, which I thought Jeff didn't like
    in building a wire cantenna.

    Bob Alston's coffee can
    Clarence Dold's coffee can
    dold, Apr 19, 2007
  6. 3.5 inches might be a good length. With dish feeds, the idea is to
    design the feed illumination angle so that it exactly covers the dish
    area. No more, no less. In this case, there's no interest in
    maximizing the gain because the dish does most of that, not the feed.
    However, if he were trying to squeeze every last dB of gain out of the
    antenna, feed gain would be important.

    See 6.3.1 above for details on the spillover (overspray) problem
    and the introduction at:
    for general clues.

    New stuff:
    Just inside the mouth of the can is at the focal point. The exact
    location is the "phase center" of the feed. See fig 6.1-1 in:
    I gave up trying to calculate the exact location and just move the
    feed in and out until the gain is at maximum.
    I have a DWL-120 (somewhere) which is what the author used. It looks
    like a loop antenna, but it's not. It's just a 1/4 wave (3.13cm)
    piece of wire inside the plastic loop. The problem is that I don't
    remember which side of the loop had the antenna. If I get ambitious,
    I'll tear it apart and see. Meanwhile, you're correct. The antenna
    is *NOT* in the center of the loop and therefore in the canter of the
    can. That will cause a lopsided illumination pattern.
    My (paper) coffee can:
    I could probably scale the model to match the tin can in the DBS dish
    construction, and see how it looks. (yet another project).

    My hacked version of Ivor Hewitt's Excel spreadsheet for generating an
    NEC2 "card" suitable for feeding to 4NEC2 antenna modeling software:
    Unfortunately, it has some problems that I've been too lazy (or too
    inept) to fix. Caveat Emptor and let me know if you find any (more)
    Jeff Liebermann, Apr 19, 2007
  7. My usb device started fruiting out and was very unstable after 2 repeaters.
    I had to run a 2nd wire for the power.

    Forster Tuncurry, Apr 19, 2007
  8. Arithmetic failure, not karma failure.

    Let's play with the numbers....

    You have a USB device that sucks perhaps 450ma at 5VDC at the end of
    perhaps 25m of USB cable (5 lengths of 5m cable). Amplifiers take
    care of data loss but not the DC power loss. Good USB cable uses
    #20AWG stranded wire at 0.034 ohms/m. Cheap junk super flexible cable
    uses #28AWG stranded at 0.232 ohms/m and isn't even worth calculating.
    Also, each gold plated connection in line will also lose about 10mv.

    So, the IR loss for #20 is:
    2 wires * 25 m * 0.034 ohms/m * 0.45A = 0.77 VDC
    Add to that the connector losses:
    2 * 5 connectors * 0.01 v/connector = 0.10 V
    for a total loss of 0.87 VDC. That means your USB radio would need to
    run off about 4.1VDC, which probably won't work. I've played with
    older USB radios and found that they'll sorta work at 4.5VDC, but tend
    to do weird things. For example, since they draw more power in xmit
    than in receive, it usually finds access points, but fails to connect.
    The newer USB radios are actually 3.3VDC devices internally, and just
    might work if the LDO (low dropout) regulator inside is doing its job.
    That might be why the WG111V2 worked and the older model did not. Next
    time I have an opportunity, I'll put a few USB radios on an adjustable
    voltage power supply and see what happens.
    Jeff Liebermann, Apr 19, 2007
  9. A quick test on the ground showed all well, but after i installed everything
    and ran cables thru the roof,down walls, ect.. i got the problems >.< my
    WG111 seems to draw the max current for a port so it needed a little help
    after the active cables chewed off a little current. The WG111v2 seems
    stable without the help but its useless for long distance links. The extra
    wire was only thin but did the job.

    Prolly karma for something.....


    > wrote in message
    Forster Tuncurry, Apr 19, 2007
  10. Sorry not exactly right. It was just a bad guess at current drain. Both usb
    cables ortho are the same make have different guage cable for the power go
    figure. The WG111v2 dies just below 4.4volts so i found.

    You fergot to factor in the weathering of the connectors...

    The local ham radio club noticed a spike in current drain when a can was
    used. could you factor that in too?

    Forster Tuncurry, Apr 20, 2007
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